The present invention relates to an electronic monitoring and/or control system for a utility vehicle, such as an agricultural tractor, equipped with a power-take-off (PTO) shaft or shafts.
PTO shafts are provided on eg agricultural tractors as a source of power for an implement mounted on or towed by the tractor, as is well known. The shaft protrudes from the rear of the tractor, and often a further shaft from the front. It is formed with splines at its protruding end to enable a rotary driving connection to be made with an implement.
Several standard types of PTO shaft are generally available, of different diameter and having different numbers of splines. Implements will generally be designed to be compatible with one or more of these standards. Each standard type also has a specific speed or speeds at which it is designed to be driven.
Generally, a tractor will be built with one type of shaft fitted and this may simply be retained for the life of the tractor. However, it is also frequently necessary to change PTO shaft type to accommodate different implements. When one shaft is substituted for another, if the design operating speed is different, the new shaft may be installed so that it is in driving connection with a different ratio in a PTO gearbox. This enables different design PTO speeds to be achieved with the same optimum engine revs. A cab mounted control may also be provided for changing the PTO gear ratio so that the design speed is achieved at lower engine revs for economy (eg for driving a light implement).
A problem with PTO shafts generally is the control of the rate at which drive to the PTO is engaged. Operating a switch on the tractor engine/transmission electronic control unit will engage drive to the PTO by automatically engaging a PTO clutch at a given rate. If an implement is fitted whose driven parts have a lot of inertia or for any other reason require a lot of power to get up to speed, the PTO output shaft can be heavily loaded. A particularly vulnerable part is the splines which may be damaged if the shaft is too heavily loaded. The maximum desirable loading for the PTO shaft will of course depend upon the type of shaft and normally the rate of engagement of the PTO clutch would have to be set so that the least robust type of output shaft ratio will not be overloaded at a high PTO ratio. This results in more robust types of shaft being engaged much more slowly than necessary.
It is an object of the present invention to alleviate the above problems and also to provide a greater degree of automation and operator awareness of the PTO function with consequent increased safety and convenience.